1. Field of the Invention
The present invention relates to an inkjet recording head and an inkjet recording apparatus, and more particularly to an inkjet recording head and an inkjet recording apparatus wherein maintenance can be performed by reliably removing ink that has thickened due to drying, ink with air bubbles mixed in, or other such ink that causes nozzle clogging or ejection problems from the nozzle.
2. Description of the Related Art
Conventionally, one known example of an image recording apparatus is an inkjet recording apparatus (inkjet printer) that has an inkjet head (ink discharge head) with an alignment of multiple nozzles, and that forms an image on a recording medium by discharging ink from the nozzles while moving the inkjet recording head and the recording medium relatively to each other.
Various methods for discharging ink in inkjet printers are conventionally known. One known example is a piezoelectric system, wherein changes the volume of a pressure chamber (ink chamber) by deforming a vibration plate that constitute part of the pressure chamber due to the deformation of a piezoelectric element (piezoelectric ceramic) so that controls the ink supply and the ink discharge to the pressure chamber.
In an inkjet recording apparatus, ink is supplied from an ink tank for storing ink to an ink ejection head via an ink supply channel, and the ink is ejected onto a recording medium from the nozzle of the ink ejection head. The ink used herein is preferably dried and adhered immediately upon being ejected onto the recording medium.
Ink is always filled in the nozzle of the ink ejection head so that printing can be immediately executed when a command for printing is received, and since ink ejection from the nozzle would be unstable if the ink in this nozzle dries, the ink ejection head is sealed by a cap during non-operation to ensure that the ink in the nozzle does not dry.
However, since the ink in the nozzle is exposed to air during printing, the ink dries in a nozzle that does not undergo ejection for a long period of time, and it is possible that the viscosity of the ink will increase, the nozzle will be clogged, and the nozzle will run out of ink, making ejection impossible. Therefore, purging must be performed wherein ink is forcefully ejected from the nozzle at specific intervals.
Also, ink cannot be ejected from the nozzle if air bubbles mixed in the ink supply channel accumulate in the ink ejection head or in front of the filter for removing impurities disposed in the ink supply channel and the supply of ink is blocked by these accumulated air bubbles.
In view of this, various proposals have been made in conventional practice for dealing with ink ejection failures or ejection problems due to inconstant pressure in an inkjet recording apparatus, which is the result of the thickening of ink or adhesion of insoluble components near the nozzle due to a reduction in volatile components in such ink, or of pressure loss due to air bubbles accumulated in the ink flow channel. These proposals include restoring the nozzle by suctioning from the nozzle surface side by negative pressure, applying great positive pressure from the supply side to eject (purge) thickened ink, and the like.
One known example of a measure for dealing with firm clogs in the head is to perform purging with the use of a pump or an ejection actuator, wherein an electric signal with a frequency approximate to the characteristic vibration frequency of the pressure chamber is sent to an ejection actuator to cause resonant vibration in the pressure chamber, resonant vibration is caused intermittently and repeatedly in the filled ink, and air bubbles adhering to the walls of the pressure chamber are extracted and suctioned and removed along with impurities (for example, see Japanese Patent Application Publication No. 2000-177126).
Also, the following are known structural examples for implementing measures for dealing with firm clogs in the head using a device other than a purging pump or an ejection actuator.
In one known example, an ultrasonic transducer is provided next to a common liquid chamber or an individual flow channel in the inkjet head, and ultrasonic vibration is caused in the cleaning fluid of the common liquid chamber or the individual flow channel (for example, see Japanese Patent Application Publication No. 2003-145782).
In another known example, compressed air is fed into the ink ejection channel where the clog has formed, and the ink causing the clog is expelled from the ink ejection port (for example, see Japanese Patent Application Publication No. 9-150509).
In yet another known example, after the ink chamber is formed during the manufacture of the inkjet head, purified water or a cleaning solution is supplied into the ink chamber, and cuttings and other such impurities that formed during manufacturing and adhered to the actuator are expelled from the nozzle along with the purified water or the cleaning solution (for example, see Japanese Patent Application Publication No. 9-193379).
However, the methods proposed in conventional practice have had problems in that air bubbles, impurities, thickened ink, or the like in a channel reaching from an individual flow channels to a nozzle via a pressure chamber are removed by negative or positive pressure from a location separate from any pressure chamber (ink chamber), a long flow channel extends from the pressure source to the point of application, and due to the inertia of the ink therein, an impact force cannot be applied to the location of the problem, a great number of trials are needed until the air bubbles, impurities, thickened ink, or the like are effectively removed, and the ink develops defects.
Also, the example disclosed in Japanese Patent Application Publication No. 2000-177126 has problems in that air bubbles and the like are expelled by inducing the maximum possible vibration using an ejection actuator, but the effects are limited and it is unlikely that the clogging will be sufficiently dispersed because the ejection actuator is optimized for the original ejection and an extra force cannot be produced.
Also, the example disclosed in Japanese Patent Application Publication No. 2003-145782 has problems in that costs increase in the case of a head having multiple nozzles when an ultrasonic element is to be installed in each individual nozzle.
Furthermore, the examples disclosed in Japanese Patent Application Publication Nos. 9-150509 and 9-193379 have problems in that they are designed to clean the ink chamber but are not designed to resume printing by immediately dispersing clogs when the nozzle is clogged during printing, and the restoring operation cannot be performed in real time.